西江水体悬浮物颗粒有机碳稳定同位素组成及时空变化

Particulate organic carbon-isotope composition and its spatio-temporal variability of suspended sediment in the Xijiang River, South China

通过对西江下游马口水文站多年的定点观测以及对虎门、梧州、江口等全流域多个河流断面悬浮物样品的稳定碳同位素分析,报道了近年来人类活动对西江流域影响的观测结果。研究发现:西江水体悬浮物颗粒有机碳稳定同位素组成从中游的-26.6‰到河口-19.8‰,逐渐变"重",此结果基本反映了流域植被覆盖及土壤侵蚀状况;西江马口水文站1999—2005年悬浮物样品δ13C值的季节循环值为(-23.4±1.3)‰,其波动与流域侵蚀、物源组成相关。根据观测结果,西江流域土壤侵蚀主要发生于下游以及源头区域,悬浮物稳定同位素比值较"重",而中游区域则相对较"轻"。河口地区的同位素值可能受工农业生产及生活废水影响较大,同位素值异化,其物质来源与河流上游和海洋不同。

This study aims to investigate the state of the riverine organic carbon by sampling at Hukou, Makou, Wuzhou, Jiangkou, Wuxuan, Du＇an, Zhexiang and Bajie hydrological stations in the Xijiang River under human impacts. Seasonal and spatial characteristics of stable carbon isotopic signature of particulate organic carbon （POCδ^13C） were examined based on several year study in the basin. The δ^13C of suspended matter ranged -26.6‰ to -19.8‰ from middle reaches to lower reaches. The seasonal change of POCδ^13C value examined at Makou hydrological station was about -23.4±1.3‰ from 1999 to 2005. Its value was related to drainage basin erosion and suspended matter sources. Soil erosion mainly took place at lower reaches areas of the Xijiang River drainage basin. So its carbon stable isotope was enriched in these areas, which affected by agricultural, industrial and wastewater at the estuary area. On the contrary, there was exhausted carbon isotope of POC on the middle areas.